This invention relates to apparatus for viewing photographic images previously recorded on a film-type medium and, more particularly, to such apparatus which converts film frame images to video signals for display on a video monitor, also known as a cine-video conversion system.
Film viewing mechanisms having general application such as film projection systems are well known to those of ordinary skill in the art, particularly in the field of cinematography or the like. These systems include a film transport mechanism and a projection mechanism, and typically project an illuminated image of one film frame at a time on a viewing screen or an empty wall. A constant image of one particular film frame may be viewed (as in a slide projector), or, more commonly, these systems are used to view images in motion. In particular, motion of the viewed image may be perceived by the viewer as a result of the repetitive projection of successive film frames which were originally recorded on the film in rapid succession.
Film projection systems, however, suffer from several drawbacks and limitations. One such drawback is the problem of limited brightness, familiar to anyone who has been to a movie theater. This problem is inherent in the process of projecting light over a significant distance. Another limitation of merely projecting the light image of the film frame is the fact that since the image is never "captured" by the system, either electronically or otherwise, there is no possibility of processing or modifying the image to improve its quality or its usability.
Recently, cine-video systems which convert the images recorded on film to video signals in real time have been introduced as an alternative to standard film projectors. With this type of system, the film frame images are electronically "captured", so as to be represented by electronic signals. These signals may be processed, if desired, and ultimately, they are displayed on a standard video monitor, thereby eliminating some of the drawbacks of projected images. The basics of such a cine-video system include a film transport mechanism, by which the film is loaded into the system and by which each film frame image is positioned for projection, a projection mechanism, by which the film frame image thus positioned is projected onto a video camera lens by an illuminating light source, and a video camera, by which the projected image is captured and converted to an electronic video signal.
One application of film viewing systems in general, and cine-video systems in particular, is in the medical field, and, more particularly, angiography, such as in a cardiac catheterization laboratory for producing high resolution displays on a standard video monitor from 35 mm angiographic film. In this application in particular, the lack of numerous quality and usability features, not heretofore present in either film projectors or prior cine-video systems, limits the value of these prior systems. For example, one of the major limitations of prior systems is the inability to provide for a continuously variable viewing speed (i.e., the number of consecutive film frames scanned by the film transport mechanism per second). In particular, although many of these systems allow for the viewing of motion at a few different film speeds, they generally do not provide for continuously variable speed viewing, as may be desired by the user, without loss of resolution.
Another drawback of the prior systems is their inability to electronically enhance the quality or usability of the video image. For example, and particularly in medical applications, it is often the case that the visibility of detail in the dark areas of high contrast pictures is limited. Electronic image enhancement techniques in which certain differences in brightness can be accentuated so as to provide more visibility of detail are not provided by prior systems. Although prior cine-video systems capture the image electronically and are therefore not inherently restricted from providing such capabilities as are mere film projectors, none have done so to date.
Yet another drawback of the prior systems is their high cost and inflexibility relative to the capabilities and features they provide. The manufacturing cost of mechanical designs and analog electrical circuitry implementation is far higher than the cost of digital electronics performing comparable functions. Moreover, the use of digital, programmable processors and associated software not only further reduces the cost, but also provides vastly superior flexibility, in that system functions can be added, replaced or modified easily and inexpensively. None of the prior commercially available film viewing systems, neither film projectors nor prior cine-video systems, are implemented as digital systems controlled by programmable digital processors.
A further drawback of prior systems is the lack of a direct digital video signal output, and particularly real time digital output, useful for applications such as recording on a digital VCR (video cassette recorder) or for data analysis. Whereas mere film projectors by themselves clearly cannot provide any output other than the viewable image itself, cine-video systems typically do provide video signal outputs. However, the prior cine-video systems do not provide any such output in a digital video format.
Yet another drawback of prior systems is the lack of a "Hi-line" video signal output, which allows for the images to be viewed on a multi-scan monitor for improved quality. A Hi-line video signal provides for twice the standard number of scan lines, and thereby increases the image brightness as well as the apparent resolution, and further reduces the noticeability of raster scan lines. Again, whereas mere film projectors cannot provide output signals at all, cine-video systems do; however, the prior commercially available cine-video systems have provided only standard video signal outputs.
A still further drawback of prior systems is their inability to include user-locatable "cursor" marks overlaid on the image being viewed. Particularly in medical applications, and particularly when an image is being viewed and discussed by more than one medical professional, it is often useful to be able to precisely identify one or more points of particular interest on the image. Prior film viewing systems provide no mechanism for overlaying such identifying marks on the image, and therefore manual, imprecise tools, such as a hand-held pointer, must be used.
Yet another drawback of prior systems is the lack of any ability to provide measurement information regarding the distance between a pair of points on the subject of the image being viewed. Particularly in medical applications such as angiography, portions of the images viewed represent vessels or other anatomical elements whose absolute size or size relative to other elements is of critical importance. Prior film viewing systems provide no mechanism for making such measurements accurately, and therefore a combination of guesswork and manual, imprecise tools (e.g., a ruler used to measure portions of the viewed image itself) must be used.
Still another drawback of prior systems is the lack of an electronically controlled zoom capability for increasing and decreasing the magnification of the image being viewed. Prior systems have provided only imprecise, manual zoom capabilities, if at all.
These aforementioned drawbacks of prior film viewing systems, both film projectors and prior cine-video systems, reduce the effectiveness and flexibility with which one may view and make use of photographic images recorded on film. Particularly in medical applications such as angiography, the elimination of these drawbacks can provide for a far more powerful tool for film viewing and analysis for the professional user.